Increasingly large and complex machine tools are being utilized in virtually all manufacturing disciplines to achieve gains in productivity and quality. These machine tools frequently have several critical components, each of which have two or more degrees of freedom. Each of these critical components must be accurately aligned or registered to a predetermined datum in three dimensional space for the machine tool to perform with maximum accuracy and repeatability.
Often times, however, the numerous degrees of freedom render the alignment or registration process excessively complex such that the adjustments to bring a machine tool into alignment are difficult (and sometimes impossible) for a mechanic, tradesperson or engineer (referred to hereinafter as simply “technician”) to visualize or determine on the shop floor. Furthermore, we have found that attempts to adjust the alignment or registration of a machine tool's critical components given only the output of the machine tool can (and often times do) produce undesired results.
With reference to FIGS. 1 and 2 of the drawings, an exemplary extrusion press is generally indicated by reference numeral 10. The extrusion press 10 is illustrated to be a direct tube extrusion press having a stationary mandrel of the type that is commercially available from SMS Hasenclever and which is employed for producing cylindrical lengths of copper tubing. Those skilled in the art will appreciate, however, that the use of an extrusion press and the fabrication of copper tubing is merely exemplary and that the teachings of the present invention have applicability to various other machine tools and to the manufacture of various other products. Accordingly, those skilled in the art will understand that the scope of the present invention is not limited by the exemplary illustration and discussion of either an extrusion press or the manufacture of copper tubing.
In the example provided, the extrusion press 10 includes a primary frame or main structure 20, a main ram 22, a moving crosshead 24, a piercing crosshead 26, a piercer ram 28, a container 30 and a die set 32. The main structure 20 includes a front platen 40, a rear platen 42, a plurality of pre-tensioned tie rods 44, and an interior structure 46 that defines a plurality of ways 48 on which the container 30 and the moving crosshead 24 translate. The main structure 20 is constructed such that the front and rear platens 40, 42 are approximately parallel to one another, being spaced apart by an appropriate distance (e.g. 25 feet) and generally perpendicular to the longitudinal axis 50 of the extrusion press 10.
The main ram 22 is associated with the rear platen 42 and is operable for translating the moving crosshead 24 along the ways 48 between the front and rear platens 40, 42. The moving crosshead 24 includes a generally hollow body 60, a stem tooling set 62 and a plurality of support feet 64. The hollow body 60 houses the piercing crosshead 26 and the piercer ram 28. The stem tooling set 62 includes a generally hollow stem 68 that includes a pressing face 70 that is generally perpendicular to the longitudinal axis of the stem 68. The support feet 64 are coupled to the body 60 and include jack screws 72a, 72b or a similar adjustment means through which the orientation and position of the body 60 may be positioned relative to the ways 48. In practice, the massive weight of the body 60 biases the jack screws 72a on the lower half of the body 60 into contact with their associated ways 48, while the jack screws 72b on the upper half of the body 60 are adjusted so as to inhibit upward movement of the body 60 during the operation of the extrusion press 10.
As noted above, the piercing crosshead 26 and the piercer ram 28 are housed in the moving crosshead 24. The piercing crosshead 26 includes a mandrel support 76, a mandrel 78 and optionally, a plurality of feet (not shown). The mandrel support 76 is disposed within a cavity in the body 60 of the moving crosshead 24 and is movable via the piercer ram 28 between an extended position and a retracted position. The mandrel 78 is coupled to the mandrel support 76 and extends forwardly therefrom through the generally hollow center of the stem 68.
The container 30 is movable along the ways 48 between a retracted position, which is rearward of the die set 32, and an extended position, which is abutted against the die set 32. The container 30 includes a hollow sleeve 80 that is configured to receive therein a billet 82 of a suitable material, such as copper.
The die set 32 conventionally includes a pressure plate, a backer and a die 32a. The die 32a is loosely coupled to the front platen 40 to permit the die 32a to move in two orthogonal directions in a plane that is generally perpendicular to the front platen 40. The die 32a includes a tapered trailing edge (not specifically shown) that matingly engages a correspondingly shaped leading edge (not specifically shown) that is formed into the sleeve 80 of the container 30. This degree of freedom, in theory, facilitates precise alignment of the die 32a to the container 30 at the beginning of an extrusion cycle.
As those skilled in the art will appreciate, the output of the extrusion press 10 (i.e., the accuracy and repeatability of the tubing produced by the extrusion press 10) is a function of the alignment of the various critical components to one another. For example, if the axis of the mandrel 78 were to be shifted relative to the axis of the stem 68 (i.e., generally parallel but not coincident), the tubing produced by the extrusion press 10 may be uniformly eccentric. In more complicated scenarios where the axis of one or more the critical components are shifted out of position and/or skewed relative to another of the critical components, the product produced by the extrusion press 10 may exhibit a varying degree of non-uniformity (e.g., a varying degree of eccentricity) or in extreme cases, exhibit defects such as ruptures or breaks.
From the foregoing, those of ordinary skill in the art will appreciate the need and desirability of aligning or registering the critical components of a machine tool. In the past, the known methodologies focused on the alignment of each of a machine tool's components to a predetermined fixed datum, such as the longitudinal axis of the machine tool. With regard to the extrusion press 10, the methodology included a two-part measurement step wherein the height of each of the machine tool's components was gauged and thereafter the distance between a datum and a face of several of the machine tool's components was employed to determine the amount by which the component was offset in a lateral direction from the longitudinal axis of the extrusion press 10. In the latter part of the measurement step, the datum comprised a wire that was stretched between the front and rear platens 40, 42 by the technician conducting the measurement.
The theory behind such methodologies is logical enough—place every component into its “design” position and the machine tool will operate in its intended manner. Unfortunately, such processes are typically very time consuming and as we have found, at times costly and complicated.
With respect to the extrusion press 10, we have found that the measurements taken for the known calibration processes often require upwards of eight hours to perform and that the results obtained in this step are generally less accurate and repeatable than is desired {for example, we estimate that the accuracy of the measurements of the distance between the datum and the faces of the machine tool's components to be within about 1 mm (0.039 inch), while the repeatability of such measurements are estimated to be within about 0.5 mm (0.019 inch)}.
The corrective action to position the various components of the extrusion press 10 into their “design” position can be extremely complicated due to the number of components that are involved, the interactions between these components, and the several degrees of freedom of each of these components. The variance between the actual position of a component and its “design” position is sometimes the result of wear, which in some situations, cannot be “adjusted” or otherwise compensated for without costly rebuilding of the extrusion press 10.
In view of the aforementioned issues, there remains a need in the art for a methodology that permits a technician to quickly and accurately determine the condition of the machine tool through the evaluation of the alignment of the various critical components of the machine tool. Further, there remains a need in the art for determining the critical components of a machine tool and for quickly and accurately aligning the critical components of a machine tool.